Continuing investigations using chromosome rearrangements concern the behavior of insertions, inversions, and duplications, and the mechanisms by which duplicate segments are spontaneously deleted. Additional duplication-generating rearrangements are being sought that will enable duplications to be constructed for the few remaining segments of the genome where this cannot now be done; duplications are needed because diploids and disomics in Neurospora are too unstable for most purposes.--Conditional lethal mutants are being screened in a search for replication or repair-defective strains and for chromosome rearrangements that exert a position effect on gene expression. --Variants affecting meiosis and ascus development are being analyzed genetically and cytologically. A possible role of histidine in recombination and repair in eukaryotes is suggested by Neurospora mutants with simultaneous defects in histidine- and radiation-sensitivity, duplication stability, and meiosis. Additional mutants known to possess one or more of these properties are being tested, and the mechanism of histidine sensitivity is being examined.--New systems are being developed for measuring intragenic mitotic recombination in heterozygous duplications.--Tests are being devised for a model relating chiasma interference to molecular models of recombination.--Spore-Killer genes that show segregation-distortion were recently discovered among wild-collected Neurospora isolates; these are being studied genetically and cytologically.